It's a pretty simple feat, Tankmon was training his lasers firing and they ended up out of cyberspace and manifesting in the Real World through Digital Waves. These lasers were doing things in the city to burn and so Takumi had to go after them to find out what was going on. In the middle of that several times Takumi deviated from the lasers issued by Tankmon and in the end he even accompanied a laser to enter it through Connect Jump.
Here you can see the mentions of the laser being compared to the rays of the sun and here you can see Kyoko's explanation of why they were real lasers, photons, instead of other things like ultrasonic waves and phonons.
Takumi appears to be between 16 and 17 years old and the average height of Japanese at this age is 170.5 cm.
In the CS scenes we only see a small part of Takumi's body, let's see the size of Takumi that appears in the scenes.
Takumi Body in cutescene = (170.8/1476) x 645 = 74.6382113821 cm
2atan(tan(70/2)*(689/756)) = 0.815271477 rad
Degrees = (0.815271477 x 180) / pi = 46.7116147895 degrees
Distance = 86.422 cm
Reaction Time = Distance / Speed
Reaction Time = 0.86422 m / 299792458 m/s = 2.88272762e-9 seconds.
To find out the distance that Takumi traveled to divert from the laser I would need to know the distance between the position of the same point in the two scenes. Unfortunately this is almost impossible to find with absolute accuracy, so just to take a test I'm going to use the most unlikely part of Takumi's body to do the calculation, the top of his hair (Since this point is the easiest to identify in the two scenes).
Distance = (74.6382113821 cm/674) x 254 = 0.281277533 meters Speed = 0.281277533 meters / 2.88272762e-9 seconds = 97573399.3 m/s or 0.325469827c (Relativistic)
RELATIVISTIC DIGIMON HUMANS